On-line libraries   

BIDS

http://www.bids.ac.uk

The British Library

http://www.bl.uk/

BVS Virtual Health Library

http://www.bireme.br/bvs/l/ihome.htm

The Cochrane Library

https://www.cochrane.org

US National Library of Medicine

http://www.nlm.nih.gov/

WHO Library

http://www.who.int/html